Abstract: The different forms of cyanobacterial bio-substances on the growth and photosynthetic activityof submerged macrophyte Ceratophyllum oryzetorum K om was investigated in present study. Results showed that all kinds of cyanobacterial bio-substances ould enhance the growthof C. oryzetorum K om. differently. Compared with the control, the plant lengthof C. oryzetorum could be increased by all forms of bio-substances, in which the dry algal material has the strongest effect, while the decomposed material has the lowest. The fresh weight of C. oryzetorum also could be promoted by all kinds of algal bio-substances, in which the dry algal material and the fresh algal material almost have the same obvious effect, and the decomposed algal material has the lowest, while in control, the fresh weight firstly increased, and then decreased. All forms of cyanobacerial material could promote the increase of branches in C. oryzetorum, in which the fresh algal material has the strongest effect and the dry and decomosed materials lower, while in control, the branches increased also less than the algal material treated groups. The photosynthetic activity expressed by chlorophyll fluorescence suggested that the dry algal material treated C. oryzetorum had the highest activity, and the fresh algae treatedone lower, and the decomposed algae and the control treatedones were the lowest. In conclusion, the different forms of cyanobacterial bio-substances could supply nutrients or growth promotersfor C. oryzetorum to grow, and at the same time, other growth inhibiters might exist to inhibit the growth of C. oryzetorum. Factors of promoting and inhibiting worked together, thus resulted in the different promoting effects by different forms of cyanobacterial bio-substances to the growth in C. oryzetorum.